Abstract's details
An Investigation of the Impact of Vertical Water Particle Motions on Fully-Focused SAR Altimetry
CoAuthors
Event: 2019 Ocean Surface Topography Science Team Meeting
Session: Instrument Processing: Measurement and Retracking
Presentation type: Type Oral
Contribution: PDF file
Abstract:
SAR altimeter processing became possible with the Synthetic Aperture Radar (SAR) Interferometric Radar Altimeter (SIRAL), which was launched on board of CryoSat-2 in April 2010. SAR altimetry, also known as Delay-Doppler altimetry (DDA), is pulse-limited in cross-track direction, just like conventional altimetry (CA), and beam-limited in along-track direction. It has therefore the potential to provide a better along-track resolution and a higher Signal-to-Noise ratio (SNR). It has been suggested that these could be further improved by applying additional phase terms; the so-called Fully-Focused-SAR (FF-SAR) processing has a theoretical along track resolution limit of half the antenna length.
However, it has been also shown that the vertical velocity of the sea surface reduces the achievable resolution in along track direction (Buchhaupt, 2019). Here we focus on deriving the second order wave spectral moment (which is the variance of the vertical velocities in a wave field) also for small sea states from CryoSat-2 full bit rate (FBR).
In the 20 Hz FF-SAR processing scheme four bursts are used here instead of the usual 160 bursts (integration time of 0.05 sec and 2 sec respectively), as this gives a similar resolution in the open ocean even for small vertical velocities of 10 cm/s (Fig. 1, right). The 20 Hz FF-SAR Delay-Doppler-Maps are retracked with a FF-SAR extension of SINCS-OV ZSK. Processed FF-SAR data are cross-compared to a reduced SAR (RDSAR) product having the same surface locations as SAR. The geophysical parameters that we compare are sea surface height, significant wave height, second order wave spectral moment and backscatter coefficient. The area of interest is the region from 30°N to 60°N and from 16°W to 10°E (North East Atlantic Box) over the year 2013.
However, it has been also shown that the vertical velocity of the sea surface reduces the achievable resolution in along track direction (Buchhaupt, 2019). Here we focus on deriving the second order wave spectral moment (which is the variance of the vertical velocities in a wave field) also for small sea states from CryoSat-2 full bit rate (FBR).
In the 20 Hz FF-SAR processing scheme four bursts are used here instead of the usual 160 bursts (integration time of 0.05 sec and 2 sec respectively), as this gives a similar resolution in the open ocean even for small vertical velocities of 10 cm/s (Fig. 1, right). The 20 Hz FF-SAR Delay-Doppler-Maps are retracked with a FF-SAR extension of SINCS-OV ZSK. Processed FF-SAR data are cross-compared to a reduced SAR (RDSAR) product having the same surface locations as SAR. The geophysical parameters that we compare are sea surface height, significant wave height, second order wave spectral moment and backscatter coefficient. The area of interest is the region from 30°N to 60°N and from 16°W to 10°E (North East Atlantic Box) over the year 2013.
